How do I create a multidimensional array from an array in Ruby?

Question

I need to create a multidimensional array from an array.

For example, let's say the initial array = [1,2,3,4,5,6]

I need a multidimensional array of

[ [1],[1,2],[1,2,3],[1,2,3,4],[1,2,3,4,5],[1,2,3,4,5,6] ]

I feel like this should be so easy, but I am stuck.

Here's what I have so far, which is wrong

def solution(a)
  empty =[]
  a.each do |x|
    new_array = Array(x)
    empty.push(new_array)   
  end
  empty.reverse
end

and I've tried

def solution(a)
  empty =[]
  for i in 1..a.size
    new_array = Array(a.pop)
    empty.push(new_array)   
  end
  empty.reverse
end

Anybody have a solution or suggestion?

EDIT: I realized that I never specified whether the array will consist of more than integers. For my purposes, I am looking for a solution that will accommodate integers or strings.

builder-7000 · Accepted Answer · 2020-05-20 18:33:39Z

2

You could use flatten:

arr = []
arr = [1,2,3,4,5,6].map{ |elm| arr = [arr, elm].flatten }
arr # => [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5, 6]]

answered May 20, 2020 at 18:33

builder-7000

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Comments

Schwern · Accepted Answer · 2020-05-21 01:16:13Z

2

Assuming you want to generate lists of sequential numbers, use 1.upto(6) to iterate 6 times, then make the individual arrays by mapping with 1.upto(i).

1.upto(6).map { |i| 1.upto(i) }

This makes an Enumerator of Enumerators. These should be fine, and you'll save memory if they get large. If you want to force them to be Arrays, add to_a.

1.upto(6).map { |i| 1.upto(i).to_a }

If you want a more generic solution, use Cary's answer.

edited May 21, 2020 at 1:16

answered May 20, 2020 at 18:27

Schwern

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4 Comments

Cary Swoveland Over a year ago

Despite the question stating, "let's say the initial array = [1,2,3,4,5,6]" your solution is unrelated to the value of array; it's just a shorthand way of writing the literal [[1[, [1,2],...]. I assume array could be [1,2,3,4,5] or ['cat', 7, :dog, 3.1], and if it were the latter, the OP would want [["cat"], ["cat", 7], ["cat", 7, :dog], ["cat", 7, :dog, 3.1]]. Other answers interpreted the question similarly. David, please clarify: is the specific array [1,2,3,4,5,6] the only one of interest or do you want the array to be arbitrary in size and content, or something else?

Schwern Over a year ago

@CarySwoveland I took that to be part of the solution, not the problem. If so, replace 1.upto(6) with the initial array.

Cary Swoveland Over a year ago

Let's see what David says.

David Lee Over a year ago

Ah this is a good point. For my purposes, I will actually be dealing with non-integers. I just used integers since it was the simplest way to write my question down. I replaced 1.upto(6) with the original array, but I am realizing I should mark another answer as the solution. So sorry about the lack of clarity.

Cary Swoveland · Accepted Answer · 2020-05-20 21:28:41Z

1

arr = [1,2,3,4,5,6]

arr.size.times.map { |i| arr[0..i] }
  #=> [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5],
  #    [1, 2, 3, 4, 5, 6]]

answered May 20, 2020 at 21:28

Cary Swoveland

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Comments

mechnicov · Accepted Answer · 2020-05-20 21:07:26Z

0

The question is not quite accurate so in more general way:

def multidemensional(ary)
  ary.map { |x| 1.upto(x).to_a }
end

multidemensional([1, 2, 3, 4, 5, 6])
# => [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5, 6]]

multidemensional([2, 2, 3, 7])
# => [[1, 2], [1, 2], [1, 2, 3], [1, 2, 3, 4, 5, 6, 7]]

answered May 20, 2020 at 21:07

mechnicov

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